Decorative sheet manufacturing method for manufacturing frosted glass-like decorative sheet

ABSTRACT

A decorative sheet manufacturing method of the present invention is for manufacturing a frosted glass-like decorative sheet using an inkjet printer including a head unit provided with a plurality of nozzles for jetting liquid droplets of an ultraviolet curable ink and an ultraviolet irradiation unit that moves together with the head unit in a main scanning direction of the head unit and irradiates the liquid droplets jetted from the nozzles and landed on a main surface of a transparent base material with ultraviolet rays, the frosted glass-like decorative sheet having the transparent base material and a plurality of dots formed in a print region on the main surface of the transparent base material and formed of a cured product of the ultraviolet curable ink by carrying out inkjet printing having predetermined printing conditions in a multi-pass manner.

TECHNICAL FIELD

The present invention relates to a decorative sheet manufacturing methodfor manufacturing a frosted glass-like decorative sheet.

BACKGROUND ART

Various developments have been made so far in the technique formanufacturing a frosted glass-like decorative sheet using an inkjetprinter. As a technique of this kind, for example, the techniquedescribed in Patent Document 1 is known. Patent Document 1 describesthat a UV curable ink made of a UV curable transparent adhesive isjetted from a nozzle of an inkjet printer onto a surface of a basematerial and at the same time irradiated with ultraviolet rays to curethe UV curable transparent ink in a frosted glass tone to form asandblast-like coating film on the surface of the base material (Claim 1of Patent Document 1).

RELATED DOCUMENT Patent Document

-   [Patent Document 1] Japanese Unexamined Patent Publication No.    2008-213152

SUMMARY OF THE INVENTION

However, as a result of examination by the present inventors, it hasbeen found that there is room for improvement in terms of banding andproductivity in manufacturing a frosted glass-like decorative sheet inthe manufacturing method described in Patent Document 1.

According to the present invention, there is provided a decorative sheetmanufacturing method for manufacturing a frosted glass-like decorativesheet, using an inkjet printer including a head unit provided with aplurality of nozzles for jetting liquid droplets of an ultravioletcurable ink and an ultraviolet irradiation unit that moves together withthe head unit in a main scanning direction of the head unit andirradiates the liquid droplets jetted from the nozzles and landed on amain surface of a transparent base material with ultraviolet rays, thefrosted glass-like decorative sheet having the transparent base materialand a plurality of dots formed in a print region on the main surface ofthe transparent base material and formed of a cured product of theultraviolet curable ink, and the decorative sheet manufacturing methodincluding a printing step of forming the plurality of dots on the mainsurface of the transparent base material by carrying out inkjet printingsatisfying the following printing conditions (1) to (3) in a multi-passmanner using the inkjet printer.

(Printing Conditions)

(1) An amount of the liquid droplets jetted from the nozzles is equal toor more than 1 pl and equal to or less than 50 pl.

(2) A waiting time from when the liquid droplets jetted from the nozzlesland on the main surface to when the liquid droplets are irradiated withultraviolet rays from the ultraviolet irradiation unit is equal to orlonger than 10 ms and equal to or shorter than 5.0 s.

(3) when a liquid droplet density in the print region in a case wherethe head unit is main-scanned once in the main scanning direction isdefined as “the amount of the liquid droplets in the (1)×outputresolution in main scanning direction×output resolution in sub-scanningdirection/number of passes of the inkjet printer”, the liquid dropletdensity is equal to or more than 0.1 μl/in² and equal to or less than1.0 μl/in².

According to the present invention, there is provided a method formanufacturing a frosted glass-like decorative sheet in which theoccurrence of banding is suppressed and the productivity is excellent.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned objects and other objectives, features andadvantages will be further clarified by the suitable embodiments whichwill be described later and the accompanying drawings which will bedescribed later.

FIGS. 1A, 1B and 1C are schematic views showing an example of aconfiguration of a frosted glass-like decorative sheet according to thepresent embodiment. FIG. 1A is a top view schematically showing adecorative sheet. FIG. 1B is an enlarged view of an a region of FIG. 1A.FIG. 1C is a cross-sectional view taken along a line A-A of FIG. 1B.

FIG. 2 is a schematic view showing an example of a configuration of aninkjet printer of the present embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings. In all drawings, the same or similarcomponents are denoted by the same reference numerals, and descriptionthereof will be omitted as appropriate. In addition, each drawing is aschematic view and a dimensional ratio in each drawing does notnecessarily match an actual dimensional ratio.

In the present embodiment, the front-back, left-right, and up-downdirections will be defined and described as shown in the drawing.However, this is provided for convenience in order to briefly explainthe relative relationships of the components. Therefore, it does notlimit the direction at the time of manufacturing and use of a product inwhich the present invention is implemented.

The outline of the decorative sheet manufacturing method of the presentembodiment will be described.

The decorative sheet manufacturing method of the present embodiment iscarried out using an inkjet printer including a head unit provided witha plurality of nozzles for jetting liquid droplets of ultravioletcurable ink and an ultraviolet irradiation unit that moves together withthe head unit in a main scanning direction of the head unit andirradiates the liquid droplets jetted from the nozzles and landed on amain surface of a transparent base material with ultraviolet rays.

The decorative sheet manufacturing method uses this inkjet printer tomanufacture a frosted glass-like decorative sheet having the transparentbase material and a plurality of dots formed in a print region on themain surface of the transparent base material and formed of a curedproduct of ultraviolet curable ink.

Such a decorative sheet manufacturing method includes a printing step offorming the plurality of dots on the main surface of the transparentbase material by carrying out inkjet printing satisfying the followingprinting conditions (1) to (3) in a multi-pass manner using the inkjetprinter.

(Printing Conditions)

(1) An amount of the liquid droplets jetted from the nozzles is equal toor more than 1 μl and equal to or less than 50 μl.

(2) A waiting time from when the liquid droplets jetted from the nozzlesland on the main surface to when the liquid droplets are irradiated withultraviolet rays from the ultraviolet irradiation unit is equal to orlonger than 10 ms and equal to or shorter than 5.0 s.

(3) when a liquid droplet density in the print region in a case wherethe head unit is main-scanned once in the main scanning direction isdefined as “the amount of the liquid droplets in (1)×output resolutionin main scanning direction×output resolution in sub-scanningdirection/number of passes of inkjet printer”, the liquid dropletdensity is equal to or more than 0.1 μl/in² and equal to or less than1.0 μl/in².

According to the findings of the present inventors, in multi-pass inkjetprinting, by appropriately controlling an the amount of the liquiddroplets jetted from an inkjet ink nozzle, a curing timing of an inkjetink (that is, a “waiting time” from when liquid droplets land on a mainsurface to when the liquid droplets are irradiated with ultravioletrays), and a “liquid droplet density” of an inkjet ink on a mainsurface, it is possible to form frosted glass-like printed matter and itis possible to suppress the occurrence of band-shaped streak unevenness(banding) that regularly occurs in a main scanning direction of aninkjet printer, which in turn can improve the productivity.

In the present embodiment, the amount of the liquid droplets means anamount of ink jetted from one nozzle. In a case where the amount of theliquid droplets is less than the lower limit value of 1 pl, filling apredetermined region of a decorative sheet requires a very high outputresolution head and a huge number of passes, which can be unacceptablefor productivity. On the other hand, in a case where the amount of theliquid droplets is greater than the upper limit value, the resolutionmay be lowered and therefore the image quality may be deteriorated. Mostof the commercially available inkjet heads correspond to an amount ofthe liquid droplets of 1 pl to 50 pl.

The shape of the dot, which is a cured product of an ink, changesdepending on the “waiting time” from when liquid droplets of an inkjetink land on a main surface to when the liquid droplets are irradiatedwith ultraviolet rays. That is, in a case where the “waiting time” istoo short, the liquid droplets are cured in a state where the liquidsurface and edges are disturbed immediately after landing of the liquiddroplets, so that the obtained dot shape becomes non-uniform.

On the other hand, in a case where the “waiting time” is set to be equalto or more than the above lower limit value, the shape of landed ink canbe stably obtained and variations in the dot-to-dot spacing of ink canbe suppressed, which makes it possible to realize a frosted glass-likedecorative sheet in which the occurrence of banding is suppressed.

In addition, in a case where the “liquid droplet density” of the inklanding on the main surface is too high, the adjacent inks may beunintentionally connected to each other. Some of the liquid dropletscome into contact with each other or two or more liquid droplets areintegrated, which, in turn, results in an increased contact area of theink with respect to the main surface and a variation in dot-to-dotspacing. In a case where the inks are connected to each other, theprinted matter consisting of dots transmits light excessively, that is,the haze of the printed matter is reduced.

On the other hand, in a case where the “liquid droplet density” is setto be equal to or less than the above upper limit value, dots of ink arestably formed and variations in the dot-to-dot spacing can besuppressed, which makes it possible to realize a frosted glass-likedecorative sheet in which an occurrence of banding is suppressed and anaesthetic appearance is excellent.

Hereinafter, the decorative sheet manufacturing method of the presentembodiment will be described in detail.

FIG. 1A is a top view schematically showing an example of a decorativesheet 200. FIG. 1B is an enlarged view of an a region of FIG. 1A, andFIG. 1C is a cross-sectional view taken along a line A-A of FIG. 1B.

The decorative sheet 200 of the present embodiment is manufactured bymulti-pass inkjet printing using an inkjet printer 100 and adoptingappropriate printing conditions.

The decorative sheet 200 is a frosted glass-like decorative sheet havinga transparent base material 210 and a plurality of dots 240 formed in aprint region 230 on a main surface 220 of the transparent base material210. The plurality of dots 240 are formed of a cured product of anultraviolet curable ink.

The top view shape of the print region constituted of a plurality ofdots 240 in the decorative sheet 200 can be applied to various shapesaccording to the application by utilizing the characteristics ofon-demand printing by inkjet. The top view shape of the print region maybe a pattern shape such as a rectangle or a circle or a shape having agradation, or may be a character shape such as an alphabet character ora Chinese character. Alternatively, these patterns may be removed fromthe print region.

The decorative sheet 200 of the present embodiment can be used todecorate the surface of a base transparent member such as glass orplastic in a frosted glass tone. The decorative sheet 200 can be appliedto, for example, building members, interior members, and the like.

The decorative sheet 200 has a haze of 35% to 95%, preferably 45% to95%, and more preferably 55% to 95%. In a case where the haze is set tobe equal to or more than the above lower limit value, the frostedglass-like decorative sheet 200 having an appropriate diffusion(blurring) effect can be realized.

The decorative sheet 200 has a total light transmittance of 60% to 99%.In a case where the total light transmittance is set to be equal to ormore than the above lower limit value, the frosted glass-like decorativesheet 200 having appropriate visibility can be realized.

The transparent base material 210 of the decorative sheet 200 is notparticularly limited as long as it has light transmittance, but thedecorative sheet 200 is made of a sheet-like light-transmitting resinfilm using a resin material such as polyester, polyolefin, polyurethane,polychloroprene, vinyl chloride resin, or acrylic resin. In a case wherethe decorative sheet 200 is made of a sheet-like resin material, thetransportability of the decorative sheet 200 is improved. In addition,the decorative sheet 200 can be easily cut into any shape.

The decorative sheet 200 may include an adhesive layer provided on aback surface 250 opposite to the main surface on which a plurality ofdots 240 are formed. The adhesive layer makes it possible to attach thedecorative sheet 200 to the surface of the above-mentioned basetransparent member.

A known adhesive can be used for the adhesive layer, and knownsilicone-based adhesive and known rubber-based adhesive can be used inaddition to an acrylic-based adhesive. Thereby, a transparent ortranslucent adhesive layer can be formed.

The main surface 220 of the decorative sheet 200 on which the dots 240are formed may be one in which the surface of the transparent basematerial 210 is not subjected to a treatment, but may be one in whichthe surface of the transparent base material 210 is subjected to a knowntreatment. Examples of the surface treatment include easy adhesiontreatments of ink such as a corona treatment, a plasma treatment, aflame treatment, and a primer treatment.

Next, the details of the printing conditions of the inkjet printer 100of the present embodiment will be described with reference to FIG. 2.FIG. 2 is a schematic view showing an example of a configuration of theinkjet printer 100.

As shown in FIG. 2, the inkjet printer 100 has a carriage 110 includinga head unit 130 and an irradiation unit 150 (ultraviolet irradiationunit).

The carriage 110 can move in an outward path direction and a return pathdirection of the main scanning direction. In a case where thetransparent base material 210 is sent in an upper direction (upper sideof the paper surface in FIG. 2(a)) of the sub-scanning directionorthogonal to the main scanning direction, the carriage 110 is locatedin a lower direction (lower side of the paper surface in FIG. 2(a)) ofthe sub-scanning direction relative to the transparent base material210.

The head unit 130 and the irradiation unit 150 are parallelly arrangedin the main scanning direction in the carriage 110. The irradiation unit150 may be arranged on at least one side of the head unit 130, but maybe arranged on both sides of the head unit 130. By arranging theirradiation unit 150 in parallel on both sides of the head unit 130,printing can be carried out in either the outward path direction or thereturn path direction.

The head unit 130 includes a plurality of nozzles 120 for jetting liquiddroplets of ultraviolet curable ink.

The plurality of nozzles 120 constitute a nozzle line in which two ormore nozzles 120 are provided at predetermined intervals in thesub-scanning direction. A plurality of the head units 130 may bearranged with the expansion thereof in either the main scanningdirection or the sub-scanning direction.

The irradiation unit 150 (ultraviolet irradiation unit) includes a lamp140 that irradiates the liquid droplets jetted from the nozzle 120 andlanded on the main surface 220 of the transparent base material 210 withultraviolet rays.

The details of the printing conditions (1) to (3) in the presentembodiment are as follows.

(1) The amount of liquid droplets of inkjet ink jetted from the nozzle120 is set to be equal to or more than 1 μl and equal to or less than 50μl. The amount of the liquid droplets can be appropriately selectedaccording to the output resolution.

(2) The waiting time is defined as a time from when liquid dropletsjetted from the nozzle 120 land on the main surface 220 to when theliquid droplets are irradiated with ultraviolet rays from theirradiation unit 150. The waiting time is set to be equal to or longerthan 10 ms and equal to or shorter than 5.0 s.

The waiting time can be actually measured, but is calculated from the“distance (mm) from nozzle 120 to lamp 140/moving speed (mm/s) ofcarriage 110”, in consideration of the time until the liquid dropletsreach the main surface from the nozzle “distance (mm) between nozzle andbase material/liquid droplet velocity (mm/s)”.

By setting the waiting time to be equal to or more than the above lowerlimit value, the occurrence of banding can be suppressed. By setting thewaiting time to be equal to or less than the above upper limit value,the productivity of the decorative sheet 200 can be set within anacceptable range.

(3) The liquid droplet density in the print region 230 in a case wherethe head unit 130 is main-scanned once in a main scanning direction isdefined as “the amount of the liquid droplets in (1)×output resolutionin main scanning direction×output resolution in sub-scanningdirection/number of passes of inkjet printer”. The liquid dropletdensity is set to be equal to or more than 0.1 μl/in² and equal to orless than 1.0 μl/in².

By setting the liquid droplet density to be equal to or less than theabove upper limit value, the occurrence of banding can be suppressed. Inaddition, the decrease in haze can be suppressed. By setting the liquiddroplet density to be equal to or more than the above lower limit value,the productivity of the decorative sheet 200 can be set within anacceptable range.

In addition, even in a case where the area or speed of the inkjetprinter 100 is increased, a frosted glass-like effect can be similarlyobtained by appropriately controlling the liquid droplet density of (3)above.

Under the above printing conditions, the number of passes in amulti-pass manner is, for example, equal to or more than 4, preferablyequal to or more than 6, and more preferably equal to or more than 8. Asa result, the occurrence of banding can be suppressed. On the otherhand, the upper limit value of the number of passes is not particularlylimited, but may be, for example, 64. As a result, the decrease inproductivity can be suppressed.

In a 4-pass simple model, the output data is divided into four groups (4divisions) and 4 main scans are carried out to complete the inkjetprinting of the nozzle width in the sub-scanning direction.

Here, an example of the procedure of the inkjet printing step will bedescribed.

First, in a first pass, liquid droplets are randomly jetted onto themain surface 220 of the transparent base material 210. In this case, byappropriately selecting the surface tension of the liquid droplets, theliquid droplets in the first pass spread wet with respect to the mainsurface at the time of landing, are connected to each other, and arecured in a leveled state. As a result, a leveling layer 242 is formed.

Even in a case where the number of liquid droplets is small in the firstpass or even in a case where there is a portion where the liquiddroplets do not sufficiently spread wet and do not form a levelinglayer, liquid droplets in a second pass land on that portion and spreadwet to form the leveling layer.

The subsequent liquid droplets are then randomly jetted onto thepreviously cured product (leveling layer 242) to be cured. That is, atleast a part of the liquid droplets after the second pass is landed onthe cured product (leveling layer 242) of the liquid droplets. Byappropriately selecting the surface tension of the liquid droplets, thesubsequent liquid droplets are repelled on the leveling layer 242 toform independent convex dots 240. By repeating this procedure, a frostedglass-like decorative sheet can be formed.

A plurality of dots 240 shown in FIG. 1C are formed on the levelinglayer 242 formed on the main surface 220 of the transparent basematerial 210. In this manner, an excellent frosted glass-like decorativesheet 200 can be formed.

In a case where the surface tension of the main surface 220 of thetransparent base material 210 is moderately low, even the liquiddroplets in the first pass are repelled and are not connected to eachother, resulting in the formation of independent convex dots. Therefore,in this case, the dots 240 are directly formed on the main surface 220of the transparent base material 210.

In addition, in the above printing step, the printing conditions in eachpass may be the same or may be appropriately changed as long as thoseprinting conditions satisfy the above-mentioned (1) to (3). In additionto the printing conditions (1) to (3) above, ink conditions and otherprinting conditions may be changed in each pass during theabove-mentioned printing step.

In addition, the decorative sheet manufacturing method of the presentembodiment may have a known step in addition to the above-mentionedprinting step.

In the decorative sheet manufacturing method of the present embodiment,the above-mentioned printing step may be carried out once or may berepeated twice or more. The plurality of printing steps may becontinuously carried out, but known steps may be appropriately carriedout before and after the printing step.

Next, the inkjet ink used in the inkjet printer will be described.

The ink used may be heated to 35° C. to 60° C. Thereby, the viscosity ofthe ink jetted from the nozzle 120 can be appropriately controlled.

The liquid droplet velocity of the ink jetted from the nozzle 120 isusually controlled to 5 m/s to 7 m/s.

As the ultraviolet curable ink, it is preferable to use an ink having asurface tension of equal to or less than 25 mN/m measured at 25° C. As aresult, an appropriate light diffusion (blurring) effect can beobtained.

The integrated light amount of ultraviolet rays irradiated to the liquiddroplets of the ultraviolet curable ink landing on the main surface 220of the transparent base material 210 is equal to or more than 10 mJ/cm²and preferably equal to or more than 30 mJ/cm². Thereby, the ultravioletcurable ink can be sufficiently cured. The upper limit value of theintegrated light amount is appropriately determined according to themoving speed of the carriage 110 and the number of passes.

The ultraviolet curable ink of the present embodiment is used forforming a frosted glass-like decorative sheet, and is an ink formulti-pass inkjet printing.

The ultraviolet curable ink includes a polymerizable monomer and asurface conditioner. This ultraviolet curable ink has a characteristicthat the surface tension measured at 25° C. is equal to or less than 25mN/m.

In a case where the surface tension is set to be equal to or less than25 mN/m, not only the leveling layer can be formed with a smaller numberof passes, but also the effect that the liquid droplets jetted after theformation of the leveling layer (after curing) are repelled on theleveling layer is exhibited.

On the other hand, in a case where the surface tension is larger thanthe above upper limit value, the ink liquid droplets after next landingdo not have an effect of being repelled by the cured ink that is a base,and the ground contact area increases. As a result, adjacent dots areconnected to each other, and a frosted glass-like decorative sheetcannot be obtained.

Hereinafter, the details of the composition components of theultraviolet curable ink of the present embodiment will be described.

The ultraviolet curable ink includes a polymerizable monomer.

A compound having two or more ethylenically unsaturated groups in amolecule thereof can be used as the polymerizable monomer. Examples ofthe ethylenically unsaturated group (ethylenically double bond group)include an acryloyl group, a methacryloyl group, a vinyl group, avinylene group, a vinylidene group, an allyl group, and a vinyl ethergroup.

In the present specification, the term “(meth)acrylate” representsacrylate and methacrylate, the term “(meth)acrylic” represents acrylicand methacrylic, and the term “(meth)acryloyl” represents acryloyl andmethacryloyl.

The polymerizable monomer can include a polyfunctional monomer.

The polyfunctional monomer is constituted of a compound having two orthree or more ethylenically unsaturated groups in a molecule thereof.From the viewpoint of easy availability, a polyfunctional (meth)acrylatecan be used as the polyfunctional monomer.

Specific examples of difunctional (meth)acrylate include 1,4-butanedioldiacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate,1,10-decanediol diacrylate, 2-butyl-2-ethyl-1,3-propanediol diacrylate,diethylene glycol diacrylate, triethylene glycol diacrylate,tetraethylene glycol diacrylate, dipropylene glycol diacrylate,tripropylene glycol diacrylate, 1,3-butylene glycol diacrylate,3-methyl-1,5-pentanediol diacrylate, neopentyl glycol diacrylate,neopentyl glycol diacrylate hydroxypivalate, propylene oxide-modified(2) neopentyl glycol diacrylate, 2-methyl-1,8-octadiol diacrylate,1,9-nonanediol diacrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, andmethacrylates thereof. These compounds may be used alone or incombination of two or more thereof.

Specific examples of trifunctional or higher functional (meth)acrylateinclude trimethylolpropane triacrylate, pentaerythritol triacrylate,dipentaerythritol tetraacrylate, pentaerythritol alkoxytetraacrylate,ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate,dipentaerythritol hexaacrylate, ethoxylated trimethylolpropanetriacrylate, propoxylated trimethylolpropane triacrylate,caprolactone-modified trimethylolpropane triacrylate, pentaerythritoltetraacrylate, pentaerythritol ethoxytetraacrylate, glycerinpropoxytriacrylate, ethoxylated dipentaerythritol hexaacrylate,caprolactam-modified dipentaerythritol hexaacrylate, propoxylatedglycerin triacrylate, ethoxylated trimethylolpropane triacrylate,ethoxylated trimethylolpropane triacrylate, propoxylatedtrimethylolpropane triacrylate, and methacrylates thereof. Thesecompounds may be used alone or in combination of two or more thereof.

Among these compounds, 1,6-hexanediol diacrylate,3-methyl-1,5-pentanediol diacrylate, neopentyl glycol diacrylate,2-(2-vinyloxyethoxy)ethyl acrylate, ethoxylated trimethylolpropanetriacrylate, pentaerythritol alkoxytetraacrylate, and the like arepreferably used.

The viscosity of the ultraviolet curable ink is measured using acone-plate type viscometer, and the viscosity at 25° C. is usually equalto or more than 20 mP·s and equal to or less than 50 mP·s. By settingthe viscosity in an appropriate range, the jetting stability of the inkfrom the nozzle can be improved. If necessary, the viscosity of the inkcan be adjusted by heating the ink.

In a case where only a polyfunctional monomer having a large number ofreactive groups is used from the viewpoint of increasing the reactivityof the ultraviolet curable ink, the viscosity of the ink may increaseand therefore the jetting stability of the ink from the nozzle maydecrease.

Therefore, by using a difunctional monomer having a relatively lowerviscosity at 25° C. than a trifunctional or higher polyfunctionalmonomer, the reactivity of the ultraviolet curable ink can be maintainedwhile keeping the viscosity thereof low. In addition, by using adifunctional monomer and a trifunctional or higher polyfunctionalmonomer in combination, the viscosity of the ink can be adjusted in arange of 35° C. to 60° C.

In the present specification, the term “to” means that an upper limitvalue and a lower limit value are included unless otherwise specified.

In addition, the ultraviolet curable ink of the present embodiment maybe configured such that the polymerizable monomer does not include amonofunctional monomer.

As a result, it is possible to suppress a decrease in the reactivity ofthe ultraviolet curable ink, which in turn makes it possible to realizean inkjet ink having excellent quick curability.

The ultraviolet curable ink includes a surface conditioner.

The surface conditioner may be, for example, a silicone-based compound.Examples of the silicone-based compound include a silicone-basedcompound having a polydimethylsiloxane structure. Specific examplesthereof include polyether-modified polydimethylsiloxane,polyester-modified polydimethylsiloxane, and polyaralkyl-modifiedpolydimethylsiloxane.

Those compounds under trade names such as BYK-300, BYK-302, BYK-306,BYK-307, BYK-310, BYK-315, BYK-320, BYK-322, BYK-323, BYK-325, BYK-330,BYK-331, BYK-333, BYK-337, BYK-344, BYK-370, BYK-375, BYK-377, BYK-378,BYK-UV3500, BYK-UV3510, and BYK-UV3570 (all manufactured by BYK-ChemieGmbH); TEGO-Rad2100, TEGO-Rad2200N, TEGO-Rad2250, TEGO-Rad2300,TEGO-Rad2500, TEGO-Rad2600, and TEGO-Rad2700 (all manufactured by EvonikDegussa GmbH); and GRANOL 100, GRANOL 115, GRANOL 400, GRANOL 410,GRANOL 435, GRANOL 440, GRANOL 450, B-1484, POLYFLOW ATF-2, KL-600,UCR-L72, and UCR-L93 (all manufactured by Kyoeisha Chemical Co., Ltd.)may be used. These compounds may be used alone or in combination of twoor more thereof.

The surface tension of the ultraviolet curable ink at 25° C. is equal toor less than 25 mNm/m. Thereby, a frosted glass-like decorative sheetcan be stably formed, as described above. The lower limit value of thesurface tension is not particularly limited.

The surface tension is measured at 25° C. based on the Wilhelmy method(plate method).

In the present embodiment, the surface tension and the viscosity at 25°C. can be controlled by appropriately selecting, for example, the typeand formulation amount of each component included in the ultravioletcurable ink, and the method for preparing an ultraviolet curable ink.Above all, for example, the type and content of the surface conditioner,the use of the difunctional monomer, and the combined use of thedifunctional monomer and the trifunctional or higher polyfunctionalmonomer can be mentioned as factors for setting the surface tension andthe viscosity at 25° C. in a desired numerical range.

The ultraviolet curable ink can include a photopolymerization initiator.

The photopolymerization initiator is a compound capable of generating asubstance that initiates radical polymerization upon irradiation withultraviolet rays.

Examples of the photopolymerization initiator include benzophenone,Michler's ketone, 4,4′-bis(diethylamino)benzophenone, xanthone,thioxanthone, isopropylxanthone, 2,4-diethylthioxanthone,2-ethylanthraquinone, acetophenone, 2-hydroxy-2-methylpropiophenone,2-hydroxy-2-methyl-4′-isopropylpropiophenone,1-hydroxycyclohexylphenylketone,2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one,2-hydroxy-1-{1-[4-(2-hydroxy-2-methyl-propionyl)-phenyl]-1,3,3-trimethyl-indan-5-yl}-2-methyl-propan-1-one,isopropylbenzoin ether, isobutylbenzoin ether, 2,2-diethoxyacetophenone,2,2-dimethoxy-2-phenylacetophenone, camphorquinone, benzanthrone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, ethyl2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate,4,4′-di(t-butylperoxycarbonyl)benzophenone,3,4,4′-tri(t-butylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(t-butylperoxycarbonyl)benzophenone,3,3′,4,4′-tetra(t-hexylperoxycarbonyl)benzophenone,3,3′-di(methoxycarbonyl)-4,4′-di(t-butylperoxycarbonyl)benzophen one,3,4′-di(methoxycarbonyl)-4,3′-di(t-butylperoxycarbonyl)benzophen one,4,4′-di(methoxycarbonyl)-3,3′-di(t-butylperoxycarbonyl)benzophen one,1,2-octanedione, 1-[4-(phenylthio)phenyl]-,2-(o-benzoyloxime),2-(4′-methoxystyryl)-4,6-bis(trichloromethyl)-s-triazine,2-(3′,4′-dimethoxystyryl)-4,6-bis(trichloromethyl)-s-triazine,2-(2′,4′-dimethoxystyryl)-4,6-bis(trichloromethyl)-s-triazine,2-(2′-methoxystyryl)-4,6-bis(trichloromethyl)-s-triazine,2-(4′-pentyloxystyryl)-4,6-bis(trichloromethyl)-s-triazine,4-[p-N,N-di(ethoxycarbonylmethyl)]-2,6-di(trichloromethyl)-s-tri azine,1,3-bis(trichloromethyl)-5-(2′-chlorophenyl)-s-triazine,1,3-bis(trichloromethyl)-5-(4′-methoxyphenyl)-s-triazine,2-(p-dimethylaminostyryl)benzoxazole,2-(p-dimethylaminostyryl)benzthiazole, 2-mercaptobenzothiazole,3,3′-carbonylbis(7-diethylaminocoumarin),2-(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,2′-biimidazole,2,2′-bis(2-chlorophenyl)-4,4′,5,5′-tetrakis(4-ethoxycarbonylphenyl)-1,2′-biimidazole,2,2′-bis(2,4-dichlorophenyl)-4,4′,5,5′-tetraphenyl-1,2′-biimidazole,2,2′-bis(2,4-dibromophenyl)-4,4′,5,5′-tetraphenyl-1,2′-biimidazole,2,2′-bis(2,4,6-trichlorophenyl)-4,4′,5,5′-tetraphenyl-1,2′-biimidazole,3-(2-methyl-2-dimethylaminopropionyl)carbazole,3,6-bis(2-methyl-2-morpholinopropionyl)-9-n-dodecylcarbazole,phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, anddiphenyl(2,4,6-trimethylbenzoyl)phosphine oxide. These compounds may beused alone or in combination of two or more thereof.

Above all, for example, a photopolymerization initiator having a2-hydroxy-2-methylpropionylphenyl skeleton such as IRGACURE 127 orESACURE ONE is preferably used because it can suppress the coloring ofan ink cured product.

In a case where the ultraviolet curable ink includes titanium dioxidehaving an ultraviolet scattering effect, the photopolymerizationinitiator can include a photopolymerization initiator having a2-hydroxy-2-methylpropionylphenyl skeleton and a photopolymerizationinitiator having an extinction coefficient of equal to or more than 200ml/g·cm at a wavelength of 365 nm. By using a photopolymerizationinitiator having an extinction coefficient of equal to or more than 200ml/g·cm in combination, it is possible to suppress a decrease incurability due to a photoradical reaction. For example, OMNIRAD TPO,which has photobleaching properties (which is resistant to color byultraviolet rays) and has little odor, is preferably used. Theabove-mentioned extinction coefficient is a value measured by aspectrophotometer after being diluted with metal (or acetonitrile).

The amount of the photopolymerization initiator added is 1% by weight to20% by weight and preferably 5% by weight to 20% by weight with respectto the entire ultraviolet curable ink.

The ultraviolet curable ink can include titanium dioxide that functionsas an ultraviolet absorber. As a result, in a case where the ultravioletcurable ink is manufactured and then stored or transported or in a casewhere the ultraviolet curable ink is filled in a tank or nozzle of aprinting device, the progress of the curing reaction of the ultravioletcurable ink can be suppressed even in a case of being exposed to weakultraviolet rays irradiated from the ambient environment such as afluorescent lamp. This makes it possible to realize an ultravioletcurable ink having excellent storability and use stability.

The upper limit value of the titanium dioxide content is equal to orless than 10% by weight and preferably equal to or less than 5% byweight with respect to 100% by weight of the ultraviolet curable ink. Atthis concentration, by appropriately selecting the particle size oftitanium dioxide, the ink does not develop an opaque white color, andthickening and yellowing of the ink can be suppressed. In addition, atthe above-mentioned concentration, the amount of the photopolymerizationinitiator and the polymerizable monomer is not reduced more thannecessary, and therefore the ultraviolet curability can be maintained.

In the technical field of ink, titanium dioxide is also used as a whitepigment, but it is known that the content of titanium dioxide in a caseof being used as the white pigment is about 10% to 20% by weight withrespect to the entire ink.

On the other hand, in the present embodiment, titanium dioxide is usedas an ultraviolet absorber instead of a white pigment.

The average particle size (value measured by a transmission electronmicroscope) of titanium dioxide is equal to or more than 5 nm and equalto or less than 200 nm and preferably equal to or more than 5 nm andequal to or less than 100 nm. This makes it possible to impart ascattering effect as well as an ultraviolet absorbing effect to theultraviolet curable ink.

The titanium dioxide can be used as a dispersion liquid of titaniumdioxide previously dispersed in an ink component, in which thedispersion liquid can include a dispersant in addition to titaniumdioxide and the ink component.

Examples of the dispersant include activators such as higher fatty acidsalts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates,sulfosuccinates, naphthalene sulfonates, alkyl phosphates,polyoxyalkylene alkyl ether phosphates, phosphate ester salts,polyoxyalkylene alkylphenyl ethers, glycerin esters, sorbitan esters,and polyoxyethylene fatty acid amides; and polymer dispersants modifiedwith styrene, styrene derivatives, vinylnaphthalene derivatives, acrylicacid, acrylic acid derivatives, maleic acid, maleic acid derivatives,itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acidderivatives, and the like. In addition, these compounds may be usedalone or in combination of two or more thereof.

For example, various dispersers such as a ball mill, a bead mill, a sandmill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloidmill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and apaint shaker can be used as the above-mentioned dispersion method.

In addition, a centrifuge or a filter may be used for the purpose ofremoving the coarse-grained fraction of the titanium dioxide dispersionliquid.

The ultraviolet curable ink can include an antioxidant or apolymerization inhibitor.

Examples of the antioxidant or polymerization inhibitor include ahindered phenol-based antioxidant, a hindered amine-based lightstabilizer, a benzophenone-based ultraviolet absorber, abenzotriazole-based ultraviolet absorber, a hindered amine-based lightstabilizer, and a triazine-based ultraviolet absorber. These compoundsmay be used alone or in combination of two or more thereof.

Among these, an antioxidant such as a hindered phenol-based antioxidantis preferably used. As a result, yellowing of the ink can be suppressed.

The ultraviolet curable ink may be a non-water-based ultraviolet curableink configured so as not to include water. This makes it possible tosuppress a decrease in reactivity and storability of ink.

The ultraviolet curable ink may be a non-organic solvent-basedultraviolet curable ink configured so as not to include a non-reactiveorganic solvent. This makes it possible to suppress a decrease inreactivity of ink. Examples of the non-reactive organic solvent includeketones and alcohols.

In the present embodiment, the expression “not included” means that itis substantially not included, and a trace amount that does not impairthe object of the present invention is allowed.

The ultraviolet curable ink of the present embodiment may includecomponents other than those described above. Examples of othercomponents include a photosensitizer, a non-reactive resin, an inorganicfiller, an organic filler, a coupling agent, a tackifier, a defoamer, apigment, a pigment derivative, and a dye.

As to the method for producing the ultraviolet curable ink of thepresent embodiment, the ultraviolet curable ink is obtained by mixingthe above-mentioned individual components. After that, if necessary, afiltration process may be carried out using a filter or the like.

Although the embodiments of the present invention have been describedhereinbefore, those embodiments are merely examples of the presentinvention and various configurations other than the foregoingembodiments can be adopted. In addition, the present invention is notlimited to the foregoing embodiments, and modifications, improvements,and the like to the extent that the object of the present invention canbe achieved are also encompassed by the present invention.

Hereinafter, examples of reference embodiments will be given.

1. A decorative sheet manufacturing method for manufacturing a frostedglass-like decorative sheet, using an inkjet printer including a headunit provided with a plurality of nozzles for jetting liquid droplets ofan ultraviolet curable ink and an ultraviolet irradiation unit thatmoves together with the head unit in a main scanning direction of thehead unit and irradiates the liquid droplets jetted from the nozzles andlanded on a main surface of a transparent base material with ultravioletrays, the frosted glass-like decorative sheet having the transparentbase material and a plurality of dots formed in a print region on themain surface of the transparent base material and formed of a curedproduct of the ultraviolet curable ink, and the decorative sheetmanufacturing method including a printing step of forming the pluralityof dots on the main surface of the transparent base material by carryingout inkjet printing satisfying the following printing conditions (1) to(3) in a multi-pass manner using the inkjet printer.

(Printing Conditions)

(1) An amount of the liquid droplets jetted from the nozzles is equal toor more than 1 pl and equal to or less than 50 pl.

(2) A waiting time from when the liquid droplets jetted from the nozzlesland on the main surface to when the liquid droplets are irradiated withultraviolet rays from the ultraviolet irradiation unit is equal to orlonger than 10 ms and equal to or shorter than 5.0 s.

(3) when a liquid droplet density in the print region in a case wherethe head unit is main-scanned once in the main scanning direction isdefined as “the amount of the liquid droplets in the (1)×outputresolution in main scanning direction×output resolution in sub-scanningdirection/number of passes of the inkjet printer”, the liquid dropletdensity is equal to or more than 0.1 μl/in² and equal to or less than1.0 μl/in².

2. The decorative sheet manufacturing method according to 1, in whichthe number of passes is equal to or more than 4 in the printing step.

3. The decorative sheet manufacturing method according to 1 or 2, inwhich the ultraviolet curable ink has a surface tension of equal to orless than 25 mN/m measured at 25° C.

4. The decorative sheet manufacturing method according to any one of 1to 3, in which an integrated light amount of ultraviolet rays emitted tothe landed liquid droplets, in the printing step, is equal to or morethan 10 mJ/cm².

5. The decorative sheet manufacturing method according to any one of 1to 4, in which the transparent base material is made of alight-transmitting resin film.

6. The decorative sheet manufacturing method according to any one of 1to 5, in which at least a part of liquid droplets after a second pass islanded on a cured product of the liquid droplets in the printing step.

7. An ultraviolet curable ink for multi-pass inkjet printing, which isused for forming a frosted glass-like decorative sheet, the ultravioletcurable ink including a polymerizable monomer and a surface conditioner,in which the ultraviolet curable ink has a surface tension of equal toor less than 25 mN/m measured at 25° C.

8. The ultraviolet curable ink according to 7, including titaniumdioxide as an ultraviolet absorber, in which a content of the titaniumdioxide is equal to or less than 10% by weight with respect to 100% byweight of the ultraviolet curable ink.

9. The ultraviolet curable ink according to 8, in which the titaniumdioxide has an average particle size of equal to or more than 5 nm andequal to or less than 200 nm.

10. The ultraviolet curable ink according to any one of 7 to 9, in whichthe ultraviolet curable ink has a viscosity at 25° C. of equal to ormore than 20 mP·s and equal to or less than 50 mP·s, which is measuredusing a cone-plate type viscosity meter.

11. The ultraviolet curable ink according to any one of 7 to 10,including a photopolymerization initiator.

12. The ultraviolet curable ink according to 11, in which thephotopolymerization initiator includes a photopolymerization initiatorhaving a 2-hydroxy-2-methylpropionylphenyl skeleton.

13. The ultraviolet curable ink according to any one of 7 to 12, inwhich the polymerizable monomer includes a polyfunctional monomer.

14. The ultraviolet curable ink according to any one of 7 to 13, inwhich the polymerizable monomer does not include a monofunctionalmonomer.

15. The ultraviolet curable ink according to any one of 7 to 14,including an antioxidant.

16. The ultraviolet curable ink according to any one of 7 to 15, inwhich the ultraviolet curable ink is a non-water-based ultravioletcurable ink that does not include water.

17. The ultraviolet curable ink according to any one of 7 to 16, inwhich the ultraviolet curable ink is a non-organic solvent-basedultraviolet curable ink that does not include a non-reactive organicsolvent.

18. A frosted glass-like decorative sheet including a transparent basematerial and a plurality of dots formed in a print region on a mainsurface of the transparent base material, in which the dots are formedof a cured product of the ultraviolet curable ink according to any oneof 7 to 17.

19. The decorative sheet according to 18, including an adhesive layerprovided on a back surface opposite to the main surface on which theplurality of dots are formed.

EXAMPLES

Hereinafter, the present invention will be described in detail withreference to Examples, but the present invention is not limited thereto.

[Preparation of Inkjet Ink]

An inkjet ink (ultraviolet curable ink) was obtained by mixing andstirring raw materials in a homomixer for 60 minutes in a dry airatmosphere under shading according to formulation ratios of rawmaterials shown in Table 1, and then pressure-filtering the mixturethrough a filter having a pore size of 2 μm.

(Polymerizable Monomer)

Difunctional monomer 1: neopentyl glycol diacrylate (LIGHT ACRYLATENP-A, manufactured by Kyoeisha Chemical Co., Ltd.)

Difunctional monomer 2: 1,6-hexanediol diacrylate (LIGHT ACRYLATE1.6HX-A, manufactured by Kyoeisha Chemical Co., Ltd.)

Difunctional monomer 3: 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA-AI,manufactured by Nippon Shokubai Co., Ltd.)

Trifunctional monomer 1: ethoxylated (9)trimethylolpropane triacrylate(SR502, manufactured by Sartomer Company Inc.)

Tetrafunctional Monomer 1: pentaerythritol alkoxytetraacrylate(EBECRYL40, manufactured by Daicel-Allnex Ltd.)

(Photopolymerization Initiator)

Photopolymerization initiator 1: 1-hydroxycyclohexylphenylketone(IRGACURE 184, manufactured by IGM Resins B.V.)

Photopolymerization Initiator 2:2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one(IRGACURE 127, manufactured by IGM Resins B.V.)

Photopolymerization initiator 3:2-hydroxy-1-{1-[4-(2-hydroxy-2-methyl-propionyl)-phenyl]-1,3,3-trimethyl-indan-5-yl}-2-methyl-propan-1-one(ESACURE ONE, manufactured by Lamberti S.p.A.)

Photopolymerization Initiator 4:diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (OMNIRAD TPO,manufactured by IGM Resins B.V.)

(Additives Such as Antioxidant and Polymerization Inhibitor)

Additive 1: pentaerythritoltetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (hinderedphenol-based antioxidant: IRGANOX 1010, manufactured by BASF SE)

(Surface Conditioner)

Surface conditioner 1: polyether-modified polydimethylsiloxane(BYK-UV3510, manufactured by BYK-Chemie GmbH)

Surface conditioner 2: polyether-modified polydimethylsiloxane (BYK-307,manufactured by BYK-Chemie GmbH)

Surface conditioner 3: polyether-modified polydimethylsiloxane (BYK-378,manufactured by BYK-Chemie GmbH)

Surface conditioner 4: polyether-modified siloxane (BYK-349,manufactured by BYK-Chemie GmbH)

(Titanium Dioxide)

Titanium Dioxide Dispersion Liquid 1

30 parts by weight of fine titanium dioxide (STR-100A, rutile type,average particle size: 16 nm, manufactured by Sakai Chemical IndustryCo., Ltd.), 5 parts by weight of a dispersant (DISPERBYK-145, phosphateester salt of high molecular weight copolymer having a pigment affinitygroup), and 65 parts by weight of a monomer (LIGHT ACRYLATE 1.6HX-A,manufactured by Kyoeisha Chemical Co., Ltd.) were kneaded and dispersedtogether with zirconia beads (bead diameter: 0.3 mm) for 10 hours usinga paint shaker to obtain a titanium dioxide dispersion liquid 1 (solidcontent concentration of titanium dioxide: 30% by weight).

TABLE 1 Experimental Experimental Experimental Experimental ExperimentalExperimental Experimental Experimental Experimental Experimental UnitExample 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7Example 8 Example 9 Example 10 Inkjet Photopolymerizable Difunctionalmonomer 1 % by 50 ink monomer Difunctional monomer 2 weight 52 50 50 5050 50 50 50 Difunctional monomer 3 40 Trifunctional monomer 39.8 39.838.9 28.9 39.85 39.75 38.95 1 Tetrafunctional 35.85 49.8 39.8 monomer 1Photopolymerization Photopolymerization 4 initiator initiator 1Photopolymerization 2 2 2 2 2 2 2 2 2 initiator 2 Photopolymerization 88 8 8 8 8 8 8 8 8 initiator 3 Photopolymerization initiator 4 AdditiveAdditive 1 0.05 0.1 0.1 0.1 0.1 0.1 0.1 0.05 0.05 0.05 Surfaceconditioner Surface conditioner 1 0.1 0.1 0.1 0.1 0.1 1.0 10.0 Surfaceconditioner 2 0.1 0.1 Surface conditioner 3 0.1 Surface conditioner 4Titanium dioxide Titanium dioxide 0.1 dispersion liquid 1 Sum 100 100100 100 100 100 100 100 100 100 Surface tension mN/m 22.7 23.7 21.6 22.722.6 21.7 21.5 24.5 24.0 22.3 Viscosity at 25° C. mPa · s 24.6 23.8 23.327.9 27.5 28.3 34.0 27.6 28.7 28.8 Ink stability Thickening A A A A A AA A A A Yellowing A A B A A A A A A A Ink curability A A A A A A A A A AExperimental Experimental Experimental Experimental ExperimentalExperimental Experimental Experimental Experimental Unit Example 11Example 12 Example 13 Example 14 Example 15 Example 16 Example 17Example 18 Example 19 Difunctional monomer 1 % by Difunctional monomer 2weight 50 49 50 50 50 50 50 50 45 Difunctional monomer 3 Trifunctionalmonomer 29.95 39.8 39 40 39.9 39.95 39.94 29.95 29.8 1 Tetrafunctionalmonomer 1 Photopolymerization 10 8 initiator 1 Photopolymerization 2 2 22 2 initiator 2 Photopolymerization 8 8 8 8 8 8 8 initiator 3Photopolymerization 2 2 2 initiator 4 Additive 1 0.05 0.1 1.0 0.05 0.050.05 0.1 Surface conditioner 1 0.1 0.1 Surface conditioner 2 10.0Surface conditioner 3 0.01 Surface conditioner 4 10.0 Titanium dioxide1.0 0.1 15.0 dispersion liquid 1 Sum 100 100 100 100 100 100 100 100 100Surface tension mN/m 21.8 23.0 36.1 36.0 36.1 36.1 29.8 27.5 22.8Viscosity at 25° C. mPa · s 37.6 28.4 27.6 27.0 27.6 27.5 27.5 25.7 25.1Thickening A A A C A A A A A Yellowing A A A C A A A A A Ink curabilityA A C A A A A A A

The obtained inkjet ink of each of Experimental Examples was evaluatedbased on the following evaluation items. The results are shown in Table1.

(Surface Tension)

The surface tension (mN/m) of the obtained inkjet ink at 25° C. wasmeasured using a surface tensiometer (Model: CBVP-Z, manufactured byKyowa Interface Science Co., Ltd.).

(Viscosity)

The viscosity (mPa·s) of the obtained inkjet ink at 25° C. was measuredusing a cone-plate type viscometer (TV-22, manufactured by Toki SangyoCo., Ltd.) under the conditions of a shear rate of 192 s⁻¹ and arotation speed of 50 rpm.

<Stability>

After exposing the obtained inkjet ink to ultraviolet rays at an amountof 5 μW/cm² for 24 hours, the presence or absence of viscosity change(thickening) and coloring (yellowing) of the ink was observed.

Using the above (viscosity) measurement method, the case where the rateof change in viscosity before and after irradiation with ultravioletrays was within 10% was marked with A, and the case where the rate ofchange in viscosity exceeded 10% was marked with C.

Regarding the ink after irradiation with ultraviolet rays, the casewithout visual observation of yellowing was marked with A, the case withvisual observation of slight yellowing was marked with B, and the casewith visual observation of yellowing was marked with C.

<Curability>

The obtained inkjet ink was appropriately heated using an inkjet printer(PatterningJET, manufactured by Tritek Co., Ltd.) and an inkjet head(KM512MH, manufactured by Konica Minolta, Inc.) and jetted onto a PETfilm subjected to an easy adhesion treatment (COSMOSHINE A4300,manufactured by Toyobo Co., Ltd.) at an output resolution of 720×720 dpiand a printing rate of 100% (solid printing). This was followed bycuring under the condition of an integrated light amount of 1000 mJ/cm²using an ultraviolet irradiation device (high-pressure mercury lamp 120W/cm, manufactured by Eye Graphics Co., Ltd.), thereby producing a curedproduct.

The surface of the obtained cured film was observed by touch with afinger, and the curability was evaluated by the case having nostickiness (tack) as being marked with A and the case having stickinessas being marked with C.

Based on the results in Table 1, it was found that the inkjet inks ofExperimental Examples 1 to 12 and 15 to 19 were superior in inkstability and curability as compared with those of Experimental Examples13 and 14. The inks of Experimental Examples 13 and 14 could not be usedas inks as evaluated.

Next, using the ink of each of the Experimental Examples, a frostedglass-like decorative sheet was produced as described later.

[Production of Decorative Sheet]

First, an inkjet printer with an ultraviolet irradiation device (CoolArcCool CA300, high-pressure mercury lamp 200 W/cm, irradiation width insub-scanning direction: 300 mm, irradiation width in main scanningdirection: 90 mm, manufactured by Baldwin Technology Company Inc.)installed in a main scanning direction was prepared.

The inkjet ink of each of Experimental Examples 1 to 12 and 19 in Table1 was jetted onto a transparent base material A or B in Table 2according to the multi-pass printing conditions (drive frequency,carriage speed, liquid droplet amount, output resolution, waiting timeuntil irradiation, and number of passes) in Table 2, irradiated withultraviolet rays, and cured to obtain a decorative sheet in which aplurality of dots were formed on the main surface of the transparentbase material.

Similarly, the inkjet ink of each of Experimental Examples 1 and 15 to18 in Table 1 was printed according to the conditions in Table 3 toobtain a decorative sheet.

In the multi-pass inkjet printing, liquid droplets were randomly jettedonto the main surface of the transparent base material under theconditions that the appropriate number of liquids in each pass was thesame and the printing rate was 100% (solid printing).

(Transparent Base Material)

Transparent base material A: PET film (COSMOSHINE A4300, both surfacessubjected to easy adhesion treatment, surface tension: equal to or morethan 44 mN/m, manufactured by Toyobo Co., Ltd.)

Transparent base material B: PET film (product name: GUV-5105, film withadhesive layer on back surface, surface tension: equal to or less than32 mN/m, manufactured by Lintec Corporation)

TABLE 2 Unit Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Driving frequency Hz 12330 3630 1760 6670 6670 900 900Carriage Speed mm/s 435 128 62 471 471 64 64 The amount of the pl 14 1414 42 42 42 42 liquid droplets Output resolution dpi 720 720 720 360 360360 360 (main scanning direction) Output resolution dpi 720 720 720 360360 360 360 (sub-scanning direction) Waiting time until s 0.60 2.03 4.190.55 0.55 4.09 4.09 irradiation Number of passes 8 8 8 16 8 8 8 Liquiddroplet μl/in² 0.907 0.907 0.907 0.340 0.680 0.680 0.680 density by onemain scan Inkjet ink Experimental Experimental Experimental ExperimentalExperimental Experimental Experimental Example 1 Example 1 Example 1Example 1 Example 1 Example 1 Example 1 Transparent base A A A A B A Bmaterial Total light % 90 89 89 90 89 89 89 transmittance Haze % 63 6667 52 67 57 66 Banding A A A A A A A Unit Example 8 Example 9 Example 10Example 11 Example 12 Example 13 Example 14 Driving frequency Hz 1487045000 12330 12330 12330 8810 8810 Carriage Speed mm/s 525 1588 435 435435 311 311 The amount of the pl 6 13 14 14 14 14 14 liquid dropletsOutput resolution dpi 1440 720 720 720 720 720 720 (main scanningdirection) Output resolution dpi 1440 720 720 720 720 720 720(sub-scanning direction) Waiting time until s 0.50 0.013 0.60 0.60 0.600.84 0.84 irradiation Number of passes 16 8 8 8 8 8 8 Liquid dropletμl/in² 0.778 0.842 0.907 0.907 0.907 0.907 0.907 density by one mainscan Inkjet ink Experimental Experimental Experimental ExperimentalExperimental Experimental Experimental Example 1 Example 1 Example 2Example 3 Example 4 Example 5 Example 6 Transparent base A B A A A A Amaterial Total light % 89 89 89 89 89 89 90 transmittance Haze % 57 6358 65 65 62 49 Banding A A A A A A A Unit Example 15 Example 16 Example17 Example 18 Example 19 Example 20 Example 21 Driving frequency Hz 88108810 8810 8810 8810 8810 8810 Carriage Speed mm/s 311 311 311 311 311311 311 The amount of the pl 14 14 14 14 14 14 14 liquid droplets Outputresolution dpi 720 720 720 720 720 720 720 (main scanning direction)Output resolution dpi 720 720 720 720 720 720 720 (sub-scanningdirection) Waiting time until s 0.84 0.84 0.84 0.84 0.84 0.84 0.84irradiation Number of passes 8 8 8 8 8 8 8 Liquid droplet μl/in² 0.9070.907 0.907 0.907 0.907 0.907 0.907 density by one main scan Inkjet inkExperimental Experimental Experimental Experimental ExperimentalExperimental Experimental Example 7 Example 8 Example 9 Example 10Example 11 Example 12 Example 19 Transparent base A A A A A A A materialTotal light % 90 89 89 89 90 89 88 transmittance Haze % 35 61 62 59 4671 67 Banding A A A A A A A

TABLE 3 Com- Com- Com- Com- Com- Com- Com- Com- parative parativeparative parative parative parative parative parative Unit Example 1Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8Driving frequency Hz 2740 1760 6670 6670 6670 6670 900 900 Carriagespeed mm/s 87 62 471 471 471 471 64 64 The amount of the pl 14 14 42 4242 42 42 42 liquid droplets Output resolution dpi 720 720 360 360 360360 360 360 (main scanning direction) Output resolution dpi 720 720 360360 360 360 360 360 (sub-scanning direction) Waiting time until s 2.984.19 0.55 0.55 0.55 0.55 4.09 4.09 irradiation Number of passes 4 2 4 42 2 4 4 Liquid droplet μl/in² 1.814 3.629 1.361 1.361 2.722 2.722 1.3611.361 density by one main scan Inkjet ink Experi- Experi- Experi-Experi- Experi- Experi- Experi- Experi- mental mental mental mentalmental mental mental mental Example 1 Example 1 Example 1 Example 1Example 1 Example 1 Example 1 Example 1 Transparent base A A A B A B A Bmaterial Total light % 89 90 89 89 90 90 89 89 transmittance Haze % 6732 47 66 34 51 51 64 Banding C C C C C C C C Com- Com- Com- Com- Com-Com- Com- parative parative parative parative parative parative parativeExample Example Example Example Example Example Example Unit 9 10 11 1213 14 15 Driving frequency Hz 900 9460 30000 8810 8810 8810 8810Carriage speed mm/s 64 334 2540 311 311 311 311 The amount of the pl 426 14 14 14 14 14 liquid droplets Output resolution dpi 360 1440 600 720720 720 720 (main scanning direction) Output resolution dpi 360 1440 600720 720 720 720 (sub-scanning direction) Waiting time until s 4.09 0.780.008 0.84 0.84 0.84 0.84 irradiation Number of passes Liquid dropletμl/in² 2.722 1.555 0.630 0.907 0.907 0.907 0.907 density by one mainscan Inkjet ink Experi- Experi- Experi- Experi- Experi- Experi- Experi-mental mental mental mental mental mental mental Example 1 Example 1Example 1 Example 15 Example Example Example 16 17 18 Transparent base BA A A A A A material Total light % 89 90 90 90 90 90 90 transmittanceHaze % 60 38 56 9 6 17 32 Banding

The “Waiting time until irradiation” in Tables 2 and 3 was defined as atime from when liquid droplets jetted from the nozzles in the inkjethead landed on the surface of the transparent base material to when theliquid droplets were irradiated with ultraviolet rays from the lamp. The“Liquid droplet density by one main scan” was calculated from [“theamount of the liquid droplets”×“output resolution in main scanningdirection”×“output resolution in sub-scanning direction”/“number ofpasses of inkjet printer” in each of Examples/Comparative Examples].

The obtained decorative sheet was evaluated based on the followingevaluation items, and the results are shown in Tables 2 and 3.

<Total Light Transmittance and Haze>

With respect to the obtained decorative sheet, the total lighttransmittance (%) and the haze (%) thereof were measured using a hazemeter (HAZE-GAAD II, manufactured by Toyo Seiki Seisaku-sho, Ltd.).

The measured total light transmittance and haze were evaluated based onthe following criteria.

In a case where the total light transmittance is equal to or more than60%, it is determined that the light transmission is good, and in a casewhere the total light transmittance is less than 60%, it is determinedthat the light transmission is poor and a frosted glass-like effectcannot be obtained.

In a case where the haze exceeds 95%, it is determined that thevisibility is low due to opacity and a frosted glass-like effect cannotbe obtained; in a case where the haze is equal to or less than 95% andequal to or more than 45%, it is determined that a moderate frostedglass-like effect can be obtained; in a case where the haze is less than45% and equal to or more than 35%, it is determined that a frostedglass-like effect can be obtained at a level where there is no practicalproblem; and in a case where the haze is less than 35%, it is determinedthat a light diffusion (blurring) effect is low due to transparency anda frosted glass-like effect cannot be obtained.

<Visual Evaluation>

Each of the decorative sheets obtained in Examples 1 to 21 andComparative Examples 12 to 15 was placed on a surface of a printedmatter on which black characters of 10 mm×10 mm were printed, at adistance of 50 mm from the surface.

In a case of being observed through the decorative sheets obtained inExamples 1 to 18, the characters were appropriately blurred to theextent that the characters could not be discriminated, and therefore afrosted glass-like effect was obtained; whereas in a case of beingobserved through the decorative sheets obtained in Comparative Examples12 to 15, the characters could be discriminated and therefore a frostedglass-like effect could not be obtained.

The decorative sheet obtained by the same inkjet printing operation asin Example 10 using a white ink for inkjet (trade name: TIC-JET1002R-STW, titanium dioxide content: 15% by weight, average particle size: 200nm, manufactured by Tokyo Printing Ink Mfg. Co., Ltd.) including nomonofunctional monomer had a total light transmittance of 43% and a hazeof 95%, and was white and opaque in the <Visual evaluation>, which couldnot be said to be frosted glass-like at all.

<Evaluation of Banding>

The obtained decorative sheet was visually observed for the presence orabsence of banding. The case in which banding did not occur was markedwith A, and the case in which banding occurred was marked with C.

Examples 22 to 24

The same inkjet printing operation as in Example 20 was repeated twice,three times, and four times to obtain decorative sheets of Examples 22to 24. The above evaluation items were evaluated for the obtaineddecorative sheets. The obtained decorative sheets of Examples 22 to 24had total light transmittances of 89%, 88%, and 88%, respectively, ahaze of 76%, and a banding of being marked with A.

Comparative Example 16

In addition, Comparative Example 16 was carried out in the same manneras in Example 1 of Table 2, except that the “time until irradiation” waschanged to “10 s”. In Comparative Example 16, it was found that theproductivity was lowered and therefore there was a problem in practicaluse.

Comparative Example 17

In addition, Comparative Example 17 was carried out in the same manneras in Example 1 of Table 2, except that the “liquid droplet density byone main scan” was changed to “0.01 μl/in²”. In Comparative Example 17,it was found that the productivity was lowered and therefore there was aproblem in practical use.

It was found that, by producing the decorative sheets of Examples 1 to24, a good frosted glass-like printed matter (plurality of dots) couldbe formed on a transparent base material.

In addition, it was found that, in the production of the decorativesheets of Examples 1 to 21, the occurrence of banding can be suppressedas compared with Comparative Examples 1 to 11; a glass-like decorativesheet having an excellent aesthetic appearance could be realized ascompared with Comparative Examples 2, 5, and 12 to 15; and theproductivity could be improved as compared with Comparative Examples 16and 17.

This application claims priority on the basis of Japanese PatentApplication No. 2018-239033 filed on Dec. 21, 2018, the disclosure ofwhich is herein incorporated by reference in its entirety.

The invention claimed is:
 1. A decorative sheet manufacturing method formanufacturing a decorative sheet, using an inkjet printer including ahead unit provided with a plurality of nozzles for jetting liquiddroplets of an ultraviolet curable ink and an ultraviolet irradiationunit that moves together with the head unit in a main scanning directionof the head unit and irradiates the liquid droplets jetted from thenozzles and landed on a main surface of a transparent base material withultraviolet rays, the decorative sheet having the transparent basematerial and a plurality of dots formed in a print region on the mainsurface of the transparent base material and formed of a cured productof the ultraviolet curable ink, and the decorative sheet manufacturingmethod comprising a printing step of forming the plurality of dots onthe main surface of the transparent base material by carrying out inkjetprinting satisfying the following printing conditions (1) to (3) in amulti-pass manner using the inkjet printer, wherein the ultravioletcurable ink has a surface tension of equal to or less than 25 mN/mmeasured at 25° C., printing conditions: (1) an amount of the liquiddroplets jetted from the nozzles is equal to or more than 1 pl and equalto or less than 50 pl, (2) a waiting time from when the liquid dropletsjetted from the nozzles land on the main surface to when the liquiddroplets are irradiated with ultraviolet rays from the ultravioletirradiation unit is equal to or longer than 10 ms and equal to orshorter than 5.0 s, and (3) when a liquid droplet density in the printregion in a case where the head unit is main-scanned once in the mainscanning direction is defined as “the amount of the liquid droplets inthe (1)×output resolution in main scanning direction×output resolutionin sub-scanning direction/number of passes of the inkjet printer”, theliquid droplet density is equal to or more than 0.1 μl/in² and equal toor less than 1.0 μl/in².
 2. The decorative sheet manufacturing methodaccording to claim 1, wherein the number of passes is equal to or morethan 4 in the printing step.
 3. The decorative sheet manufacturingmethod according to claim 1, wherein an integrated light amount ofultraviolet rays emitted to the landed liquid droplets, in the printingstep, is equal to or more than 10 mJ/cm².
 4. The decorative sheetmanufacturing method according to claim 1, wherein the transparent basematerial is made of a light-transmitting resin film.
 5. The decorativesheet manufacturing method according to claim 1, wherein at least a partof liquid droplets after a second pass is landed on a cured product ofthe liquid droplets in the printing step.
 6. The decorative sheetmanufacturing method according to claim 1, wherein, in the printingstep, a leveling layer formed of the cured product of the ultravioletcurable ink is formed on the main surface of the transparent basematerial and the plurality of dots are formed on the leveling layer. 7.The decorative sheet manufacturing method according to claim 1, whereinthe ultraviolet curable ink includes a polymerizable monomer and asurface conditioner, and the ultraviolet curable ink has a surfacetension of equal to or less than 25 mN/m measured at 25° C.
 8. Thedecorative sheet manufacturing method according to claim 7, wherein thepolymerizable monomer includes a polyfunctional monomer.
 9. Thedecorative sheet manufacturing method according to claim 7, wherein thepolymerizable monomer does not include a monofunctional monomer.
 10. Thedecorative sheet manufacturing method according to claim 1, wherein theultraviolet curable ink includes titanium dioxide as an ultravioletabsorber, and a content of the titanium dioxide is equal to or less than10% by weight with respect to 100% by weight of the ultraviolet curableink.
 11. The decorative sheet manufacturing method according to claim10, wherein the titanium dioxide in the ultraviolet curable ink has anaverage particle size of equal to or more than 5 nm and equal to or lessthan 200 nm.
 12. The decorative sheet manufacturing method according toclaim 1, wherein the ultraviolet curable ink has a viscosity at 25° C.of equal to or more than 20 mP·s and equal to or less than 50 mP·s, asmeasured using a cone-plate type viscosity meter.
 13. The decorativesheet manufacturing method according to claim 1, wherein the ultravioletcurable ink includes a photopolymerization initiator.
 14. The decorativesheet manufacturing method according to claim 13, wherein thephotopolymerization initiator includes a photopolymerization initiatorhaving a 2-hydroxy-2-methylpropionylphenyl skeleton.
 15. The decorativesheet manufacturing method according to claim 1, wherein the ultravioletcurable ink includes an antioxidant.
 16. The decorative sheetmanufacturing method according to claim 1, wherein the ultravioletcurable ink is a non-water-based ultraviolet curable ink that does notinclude water.
 17. The decorative sheet manufacturing method accordingto claim 1, wherein the ultraviolet curable ink is a non-organicsolvent-based ultraviolet curable ink that does not include anon-reactive organic solvent.